Air flow is one of the oldest sources of energy used by man, but even today it is one of the least researched suppliers of energy. Recently, windmills have been used as a source for generating electrical energy. One advantage of wind driven power stations is their environmental friendliness. A wind utilizing power station consumes no raw materials nor does it give off waste gases or waste materials. Further, wind utilizing power devices generally produce relatively little noise in their operation.
Wind utilizing devices of the type having a turbine have been disclosed in U.S. Pat. No. 2,004,853 to Crary. Such turbines have blades or vanes attached to a rotatable shaft in which the vanes are driven by the wind. The shaft is coupled to an electric power generating device. Such wind utilizing devices are often referred to as windmills.
Some windmills have been specially adapted to increase electrical output. U.S. Pat. No. 3,720,840 discloses one such adapted windmill. These adaptations include making the position of the fluid inlet adjustable and utilizing a heating unit to increase fluid flow through the device.
Another windmill device, which has been developed by Green Energy Technologies of Cleveland, Ohio, includes a windmill that is often located on tall buildings and is positioned on a turnstile. Such windmills may include a collector or shroud that helps increase the velocity of the wind passing through the vanes of the windmill. The turnstile of such devices is typically configured to permit the windmill to move into the direction that the wind may be blowing to collect an air flow sufficient to rotate the vanes of the windmill to generate electricity.
Attempts have also been made to utilize secondary air currents in connection with windmill type devices to generate power. For example, U.S. Pat. No. 3,936,652 discloses a power plant that has air inlet ducts connected to a cooling tower. As hot air flows out of a vertical tower, the hot air is sucked into the inlet ducts. The flow of the hot air in the inlet ducts turns windmill devices provided in the inlet ducts.
More recently, a system that utilizes waste or exhaust air flow from one or more ventilation systems of a defined area, such as a mine, has been disclosed. For example, U.S. Pat. No. 5,512,788 to Berenda et al. discloses such a system. The entirety of U.S. Pat. No. 5,512,788 is hereby incorporated by reference herein. U.S. Pat. No. 5,512,788 discloses an exhaust air recovery system that utilizes wasted or exhausted air flow from one or more ventilation systems from a mine, tunnel, or other area requiring ventilation. The exhaust fan expels air causing air velocities to be directed out of the area requiring ventilation. The exhaust air from the one or more ventilation systems is captured and converted to electrical energy by one or more windmills or other devices configured to utilize an air flow to generate electricity.
The system disclosed in U.S. Pat. No. 5,512,788, however, has been found to include problems that need resolved. For example, we have conducted studies of the air flow from ventilation exhaust systems used in mines and tunnels and found that the exhaust air flow is often not a laminar flow. The exhaust stream may include a vortex in the air flow. Moreover, turbulence is often caused when the exhaust air flow impacts the earth or other objects after the air flows beyond the exhaust of the one or more ventilation systems. We have found that such turbulent flow is not necessarily ideal for recovering energy from the exhaust air flow. Further, particles from the earth or other debris may enter the air flow and be directed toward a windmill positioned to utilize the exhaust flow. Such debris may damage the windmill or increase the maintenance costs for the windmill.
We have found that a system of recovering energy from a ventilation system should include a device that can help recover the energy provided by an exhaust air flow as efficiently as possible with windmill technology. Such a device should be configured to control the turbulence and tangential flow of the exhaust air flow. The device is preferably configured so at least a portion of the exhaust air flow is redirected toward a windmill in an axial direction. Such a device and the windmill of the system are also preferably positioned far enough away from the exhaust of the one or more ventilation systems so that no back pressure on a ventilation fan or exhaust fan is created.